Circadian blood pressure variability in adrenocorticotrophin-induced hypertension in the rat

Objectives. Secondary hypertension is often characterized by loss of diurnal blood pressure variability. This study examined circadian (24 h) blood pressure variability in adrenocorticotrophin (ACTH)-induced hypertension in the Sprague-Dawley rat. Methods. Male Sprague-Dawley rats were randomly allocated to sham (0.9% saline, s.c.), n = (9), ACTH (0.5 μg/kg per day, s.c., n = 8) or ACTH (100 μg/kg per day, s.c., n = 7) in a room with a 12 h light/dark cycle (0600 h to 1800 h). A radio telemetry transducer was used to measure blood pressure in unrestrained animals over 3 control days (C1-C3) and 10 treatment days (T1-T10). Heart rate, systolic (SBP), mean arterial (MAP) and diastolic (DBP) blood pressure were continuously recorded. Body weight was measured daily and serum corticosterone concentration ([B]) prior to death. Results. Sham treatment had no effect on any parameters. ACTH 100 μg/kg per day increased SBP from 124 ± 2 pooled control (PC) to 1 34 ± 2 mmHg (T10), MAP from 105 ± 2 to 115 ± 2 mmHg and DBP from 87 ± 1 to 99 ± 2 mmHg and decreased heart rate from 305 ± 6 to 249 ± 5 beats/min and body weight from 299 ± 6 (C3) to 280 ± 8 g (T10) (all P′ < 0.0036). Serum [B] was higher in ACTH- (881 ± 44 ng/ml) than sham-treated rats (384 ± 17 ng/ml, P<0.001). There were no differences between sham treatment and ACTH 0.5 μg/kg per day. SBP, MAP, DBP and heart rate were consistently higher for ACTH 100 μg/kg per day and sham-treated animals during the dark cycle (1800 h to 0600 h) than the light cycle (0600 h to 1800 h). Conclusions. ACTH 100 μg/kg per day raises blood pressure in conscious unrestrained Sprague-Dawley rats without any change in normal diurnal rhythm.